We developed three-dimensional model of isolated myocardial mus-cular preparations that takes into account the coupling of excitation with contraction in the myocardium at the cellular and tissue levels. This model describes heart tissue using approaches and methods developed in continuum mechanics. In the model, electromechanical interactions and mechano-electric feedbacks are realized both at the micro level and at the macro level. We used non-linear partial differential equations de-scribing the deformation of the cardiac tissue, and a detailed “Ekaterin-burg-Oxford” (EO) cellular model of the electrical and mechanical ac-tivity of cardiomyocytes (Sulman et al., 2008). Electrical and mechanical interactions between the cells in the wedge model, as well as intracellular mechano-electric feedback beat-to-beat affect the functional characteristics of coupled cardiomyocytes further, adjusting their electrical and mechanical heterogeneity to the activation timing. Model analysis suggests that cooperative mechanisms of myofil-ament calcium activation contribute essentially to the generation of cel-lular functional heterogeneity in contracting cardiac tissue. This work was supported by the RFBR grant 18-31-00416.